Reducing heat-seal temperature requirements for coatings prepared from latexes of vinylidene chloride polymers

ABSTRACT

WHEREIN R1 is hydrogen or alkyl and R2 is alkyl wherein the sum of R1 and R2 equals from eight to 20 carbon atoms; where Y is hydrogen or methyl; where n is an integer from 6 to 40; and where R3 is hydrogen or methyl.   A process for reducing the heat-seal temperature requirements of films and coatings produced from high vinylidene chloride polymer latexes comprising having present in films or coatings formed from such latexes, prior to fusion thereof, from about 0.5 to about 5 percent by weight of latex polymer solids of an alkyl phenol olefin oxide adduct of the formula

United States Patent 191 Gibbs et al.

REDUCING HEAT-SEAL TEMPERATURE REQUIREMENTS FOR COATINGS PREPARED FROM LATEXES OF VINYLIDENE CHLORIDE POLYMERS Inventors: Dale S. Gibbs; Ritchie A. Wessling, both of Midland, Mich.

Assignee: The Dow Chemical Company,

Midland, Mich.

Filed: July 9, 1973 Appl. No.: 377,482

Related US. Application Data Continuation-impart of SerfNo. 202,624, Nov. 26, 1971, abandoned.

Us. Cl. 260/29.6 TA, 260/296 E, 260/296 ME, 260/296 MQ, 260/296 RB, 2691229 3? 269 22 55292292219;

Int. Cl cos 1/13 Field of Search260/29.6 TA, 29.6 E, 29.6 MQ,

260/296 so, 29.6 ME, 29.6 2, 79.3 M

References Cited UNITED STATES PATENTS 6/1967 Fikenscher et al. 260/296 TA Oct. 22, 1974 3,483,154 12/1969 Gibbs 260/296 TA 3,617,368 11/1971 Gibbs 260/296 TA X 3,701,745 7 10/1972 Settlage et al 260/296 TA X Primary Examiner-Lucille M. Phynes Attorney, Agent, or Firm-Ronald G. Brookens 5 7 ABSTRACT wherein R is hydrogen or alkyl and R is alkyl wherein the sum of R and R equals from eight to 20 carbon atoms; where Y is hydrogen or methyl; where n is an integer from 6 to 40; and where R is hydrogen or methyl.

8 Claims, N0 Drawings REDUCING HEAT-SEAL TEMPERATURE REQUIREMENTS FOR COATINGS PREPARED FROM LATEXES OF'VINYLIDENE CHLORIDE POLYMERS BACKGROUND This application is a continuation-in-part of the now abandoned application Ser. No. 202,624, filed Nov. 26, 1971.

Copolymers and interpolymers of vinylidene chloride with such comonomers as acrylonitrile, vinyl chloride, and lower alkyl acrylates have found wide acceptance as film and coating materials because of their desirable properties including transparency, inertness, ability to be heat sealed and impermeability to moisture and gases. It is also recognized that the impermeability of such film and coatings increases with an increasing concentration of vinylidene chloride in the polymer la tex. It is further recognized that such increase in impermeability it accompanied by a higher temperature requirement for producing an effective heat seal in the resulting film or coating, e.g., film and coatings prepared from a polymer containing at least about 80 percent by weight vinylidene chloride in the polymer molecule requires a temperature of at least about 160C. for effective heat sealing. This high temperature requirement is particularly undesirable where high speed commercial packaging techniques are employed.

It is the primary object of this invention to provide a means of significantly lowering the heat-seal temperature requirement for films and coatings prepared from polymers containing at least about 80 percent by weight of vinylidene chloride in the polymer molecule, without adversely affecting the impermeability and other desired properties of such film or coatings.

SUMMARY The above and related objects are attained by a process comrising the production of a polymer latex which consists essentially of water and a colloidally dispersed solid polymer prepared by the polymerization in aqueous dispersion of 1 1. at least about 80 percent by weight based on the total weight of monomers used of vinylidene chloride,

2. from about 0.1 to about 5 percent based on the total weight of the monomers used of a significantly water-soluble ionic material selected from the group of sulfonic acids and their salts having the formula wherein the radical R is selected from the group consisting of vinyl and alpha-substituted vinyl; the symbol Z represents a difunctional linking group which will activate the double bond present in said vinyl group; Q is a divalent hydrocarbon having its valence bonds on different carbon atoms; the symbol M+ represents a cation selected from the group consisting of free acids, alkali metal salts, and ammonium, amine, sulfonium and quaternary ammonium salts, and

3. any remainder being one or more monoethylenically unsaturated comonomers; wherein there is present in the films and coatings produced from such latexes, prior to fusion thereof, from about 0.5 to about 5 percent by weight of polymer solids of an alkyl phenol-olefin oxide adduct having the formula wherein R is hydrogen or alkyl and R is alkyl wherein the sum of R and R equals from eight to 20 carbon atoms; where Y is hydrogen or methyl;'where n is an integer from 6 to 40; and where R is hydrogen or methyl.

It has been unexpectedly discovered, which discovery forms a part of the present invention, that the prescribed amounts and types of such adducts, when incorporated in the monomer charge or post-added to the polymer latex, exude to the surface of film or coatings prepared from the disclosed polymer latex as the film or coating fuses and crystallizes; and that such adduct remains present on such surfaces as heat and pressure are applied during conventional heat-seal operations. Under such applied heat and pressure, however, the solubility of the adduct, in the film or coating, appears to be increased sufficiently to reduce the temperature required for attaining an effective heat seal, i.e., excellent heat seals are obtained at temperatures as low as C. as contrasted to temperatures of C. or more for films or coatings absent such adduct. Although the exact mechanism is unknown, it is known that the comonomeric emulsifier constituent used in the preparation of the prescribed polymer latexes, although providing significantly enhanced latex colloidal stability,'also results in higher heat-seal temperature requirements. It appears that the nonionic additives of this invention interact in some way with such comonomeric emulsifier to remove such detrimental characteristic.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The polymer latexes used in the present invention may be prepared in any conventional manner but are preferably prepared in aqueous dispersion by an essentially continuous, carefully controlled addition of the requisite polymerization constituents (includingpolymerization initiator systems if desired) to an aqueous medium, as per thetechniques set forth in the US. Pat. No. 3,617,368, issued Nov. 2, 1971.

More particularly, it is often preferred to first add a small amount of the monomeric materials, as defined herein, to the aqueous medium having the desired pH value, followed by the subsequent addition of the necessary polymerization initiator, to form a polymeric seed latex in order to aid in the control of particle size. When forming such polymeric seed latexes by the procedure as described herein, small amounts of conventional wetting agents such as alkali soaps or the like, may be incorporated in the aqueous medium to further aid in the attainment of particles of desired size. The addition of such wetting agents, however, is not critical for the production of the highly stable aqueous colloidal dispersion of polymeric particles.

Following the formation of the polymeric seed latex, the remaining polymerization constituents are simultaneously and continuously added under carefully controlled conditions to the aqueous medium.

The compositions, as described herein, are subjected to conditions conducive to polymerization of the polymerizable constituents. ln most instances, the temperature of the aqueous dispersion is adjusted, for example,

to aternperature between about the freezing point of the serum and 100 C. to activate the polymerization. Other means, such as exposure of the composition to active radiation can be employed to promote polymerization of the polymerizable constituents.

As described, supra, the prescribed polymer latexes are prepared from a monomer composition containing at least about 80 percent by weight vinylidene chloride,

R- -'ZQ-SO{-M+ wherein the radical R is selected from the group consisting of vinyl and a-substituted vinyl; where the symbol Z represents a difunctional linking group which will activate the double bond present in the vinyl group, e.g., groups of the structure: 7

o o o II II II I! I -c-., -c-o, '-o-c, -C-N,

and the like; where -Q is a divalent hydrocarbon having its valence bonds on different carbon atoms, eg. the alkylene' and arylene divalent hydrocarbon radicals having from one to about eight carbon atoms; and M+ is a cation. p

The solubility of the'defined copolymerizable ionic materials as described herein is strongly influenced by the cation M+. Exemplary of preferred cations are the freeacids, alkali metal salts, ammonium and amine salts and sulfonium and quaternary ammonium salts.

It is further to be noted that withone of the ions above, and the usual choices for R and Z, the solubility of the monomer depends on Q. As indicated, this group can be either aliphatic or aromatic and its size will determine the hydrophilic/hydrophobic balance in the molecule, i.e., if Q is relatively small the monomer is water soluble but as Q becomes progressively larger the surface activity of such monomer increases until it becomes a soap and ultimately a water-insoluble wax. It is to be understood, however, that the limiting size of Q depends on R, Z and M+. As exemplary of the above, it has been found that sodium sulfoalkyl methacrylates of the formula:

wherein n is 2, are highly acceptable copolymerizable ionic materials for use in the present invention.

Further, the selection of R and Z is governed by the reactivity needed andthe selection of Q is usually determined bythe reaction used to attach the sulfonic acid to the base monomer (or vice versa).

It has been found that sodium sulfoethyl methacrylate is especially effective for use.

Other monomers which readily copolymerize with vinylidene chloride, in aqueous dispersion, i.e., which copolymerize within a period of less than about hours at a temperature ranging from the freezing point of monomeric serum up to about l00 'C., and which preferably have a solubility in both the water and the oil phase of the polymer latex of at least 1 weight percent at the temperature of polymerization, may also be used in preparation of the polymer latexes used'in the present invention. Exemplary of preferred materials are methacrylic acid, methyl methacrylate, hydroxy ethyl and propyl acrylates', hydroxyethylmethacrylate, acrylic acid, acrylonitrile, methacrylonitrile, acrylamide and the lower alkyl and dialkylacrylamides, acrolein, methylvinyl ketone and vinyl acetate.

The alkyl phenol-olefin oxide adduct prescribed by the present invention may be added with the monomer charge during preparation of the polymeric latex or may be post-added following preparation of the latex, or may be coated on the surface of films or coatings prepared from such latexes, prior to fusion thereof.

Exemplary of specific adduct materials preferred for use in the present invention are the nonyl phenol, ditertiarybutyl phenol and disecondarybutyl phenol-olefin oxide condensates having from 6 to 40 moles of olefin oxide, e.g., ethylene oxide or propylene oxide and mixtures thereof.

The latexes of the present invention are particularly useful for preparing coated products comprising a wide variety of substrates having a continuous, adherent, dried coating of such latex thereon which coating has excellent barrier, flexibility, low heat-seal temperature requirement and excellent binding capacity properties.

Exemplary of the substrates which may be advantageously coated with the polymer latexes of this invention are sheets or films of: the nonaromatic hydrocarbon olefin polymers such as the polymers and interpolymers of ethylene, propylene, and butylene and the like and their halogenated derivatives; the aromatic hydrocarbon polymers such as the polymers and interpolym'ers of styrene and the like; the polyesters such as polyethylene terephthalate and the like; various polyamides such aspolyhexamethylene adipamide among others; polyimides; the halogenated ethylenepolymers such as the vinyl and vinylidene chloride homopolymers and interpolymers; polyacrylonitrile; regenerated cellulose; and the various cellulose esters such as cellulose acetate, cellulose nitrate and cellulose acetate butyrate; polyvinyl acetals; vinyl combinations such as polyvinyl chloride/polyvinyl acetate copolymers; fibrous cellulosic materials such as tissue paper, book papers, crepe paper, wrapping paper, cardboard, chipboard, wallboard and the like; metals such as aluminum and tin, amongothers; wood products such as plywood; textiles such as cotton textiles and fabrics; other vegetable fiber products; and other substrata which are relatively insoluble in the coating dispersions of the present invention. It is to be understood that the polymer latexes described herein can also be used to cast unsupported films or sheets if desired.

The following examples illustrate the polymer latexes and preparation of coated products therefrom according to this invention, but are not to be construed as lirn iting its scope. in the examples, parts and percentages are by weight unless otherwise indicated. I

EXAMPLE 1 lnto a polymerization vessel was charged a mixture of 500 grams of deionized water (adjusted to pH of 3.5 with glacial acetic acid) and 2.5 grams of sodium dode cyl benzene su1fonate. To this mixture was subsequently added an initial monomer charge comprising each admixture allowed .to stand overnight. The admixtures were then each coated on separate portions of a substrate composed ofglassinepaper having thereon a topcoat of asoft vinylidene chloride polymer. Each 46 grams of vinylidene chloride, 4 grams of acryloni- 5 coated sample was then aged at 140 F. for a period of ril and 0,05 gra t-b tyl hyd xid about 16 hours to permit crystallization of the applied The reaction mixture was then stirred under nitrogen inylid ChlOrlde l After g g. the h at-Sea alfor a period of 20 minutes at a temperature of 30 C., ues for each coated sample were determined, as grams and a solution comprising 2.7 grams of sodium formalper mch width, after each coated sample had individudehyde sulfoxylate in 500 grams aqueous solution was y been Subjected to a P1615511re of 20 P for a P 10d thereafter added to the reaction mixture at a rate of 7.7 of 1 Second finder normal room mpe resgrams of solution per hour until polymerization of the The emulsifiers used have the followmg deslgnatlons initial charge of monomers was completed. Following and stfucturesi completion of polymerization of the initial charge of monomeric materials, a second monomeric mixture comprising 1,012 grams of vinylidene chloride, 88 Em ulsifier grams of acrylonitrile and 1.1 grams of t-butyl hydro- Dmgndm peroxide Was added to the polymerizatiOn Vessel A Sodium salt of dodylbenzen sulfonale 'n a rate of 55 rams of the mixture er hour for B sodium lauryl Sulfate stun t a g p C Sodium salt of disult'onated alkylbiphenyl a period of 20 hours. Over the same period of time, a Oxide solution comprising 17.6 grams of sodium sulfoethyl D g of g y Phenol with 10 moles O C cne OX1 e methacrylate m 3oo'grams of f q f solutlon was E Addud t of di-t-butyl phenol with 40 moles arately added to the polymerization vessel at a rate of ofcthylene oxide v 15 grams of solution per hour. Following the addition F 2211 f g gfss zila of the polymerizable materials, the herein described G Adductofnonyl phenol with 6 moles of ethylene oxide 7 aqueous solution of sodium formaldehyde sulfoxylate H Addum ofnony] phenul with 10 moles of was added to the polymerization vessel at the pre- WW flelhyiggevofm I established rate for a period of 2 hours, to allow com- I g of ng y phenol with moles of C! y ene 0X1 6 pletion of polymerization of the monomeric constitu- 30 J Add! dummy hum phenol with ents. The resulting polymerization product was a highly 4 moles of ethylene oxide and 4 moles colloidally stable, low-foaming, aqueous colloidal poly- Pmpylec mer dispersion containing approximately to 52 percent polymer solids prepared from a total monomer 4 charge of about 92 parts by weight of vinylidene chlo- Th OIIO mg Table I Sets forth the types and ride, about 8 parts by weight of acrylonitrile and about 35 amounts of emulsifiers used and the heat-seal values 1.6 parts by weight of sodium sulfoethyl methacrylate. obtained:

TABLE 1 Exp. No. Emulsifier Heat Seal (Gmslin. width] Type Amount C. C. C.

#71 by wt. of polymer solids) For Comparison 1 None 0 0 0 2 A 0.5 5 e 18 3 A 10 5 s 16 4 B 0.5 4 5 a 5 B 1.0 6 c 0.5 2 a 24 7 c 1.0 2 6 16 The Invention 8 D 0.5 14 80 Substrate lear" 9 D 1.0 16 Substrate tear 10 E 0.5 20 1 I E 1.0 15 250 Substrate tear 12 F 0.5 27 54 135 13 F 1.0 31 83 Substrate tear 14 o 0.5 s 42 100 15 o 1.0 24 42 16 H 0.5 10 4s 76 17 H 1.0 20 Substrate tear 18 l 0.5 7 20 57 I9 1 1.0 18 70 Substrate tear 20 J 0.5 10 46 1x0 21 J 1.0 46 Substrate tear 'Seal strength exceeds strength of the substrate.

Thereafter,in each of a series of experiments, one of several emulsifiers were admixed, at varying concentrations,-to individual portions of the polymer latex and The data from Table 1 illustrate the significantly enhanced low temperature heat-seal characteristics obtained using the emulsifiers prescribed by the present .hsakssal ra lies Qtt EXAM LE A polymeric latex, the polymersolids of which were prepared from a monomer composition of about 92 parts by weight vinylidene chloride, about 5.5 parts by weight acrylonitrile, about 2.5 parts by weight methyl methacrylate and about 1.4 parts by weight of sodium sulfoethyl methacrylate, was prepared essentially as per the technique set forth in Example 1. 1n each of a series of individual experiments varying amounts of an adduct of nonyl phenol with 10 moles of ethylene oxide was added to the latex. The latex, containing 40 percent of polymer solids, was then applied as a coating to glassine paper and the heat-seal strength determined essentially as set forth in Example 1. The following Table 11 proi'ides the types and amounts of adduct used and the 6 stated substrate TABLE ll TABLE 11! Sulfonic Acid Emulsifier MHST Sample No. Salt by wt.) by wt.) (C.)

none none 135- l 40 26 none 3 130 27 1.4 none 140 The Invention Series B The experiments as described in Series A above were repeated utilizing a polymer latex, the polymer solids of which were prepared from a monomer composition of about 80 parts by weight vinylidene chloride, about 15 parts by weight butyl acrylate, about 5 parts by weight acrylonitrile and about 1.6 parts by weight of sodium sulfoethyl methacrylate. The following Table IV sets forth the presence or absence of the sulfonic acid salt and the alkyl phenol olefin oxide adduct, as well as the Adduct Amount (7n by wt. of. I Heat Seal Gms.[in. width) Experiment No. polymer solids) 100C. 1 10C. 120C. 130C.

For Comparison 22 0 0- O O 73 The invention 23 1.0 243 695 Substrate tear 24 2.0 577 Substrate tear I EXAMPLE 3 minimum heat-seal temperature (MHST) of each Series A r coated sample.

1n each of a series of experiments, a polymer latex was prepared essentially as described in Example 11 herein but with and without the presence of the ionic, copolymerizable salt of sulfonic acid (sodium sulfoethyl methacrylate), and with and without an alkyl phenol olefin oxide adduct as an emulsifier. In those instances where such an emulsifier was present the material was an adduct of di-t-butyl phenol with 10 moles of ethylene oxide which was used in an amount of from 1 to 5 percent by weight of polymer solids. The resulting polymeric latexes, containing 40 percent by weight of polymer solids, was applied to 30 pound, white, opaque glassine in two coats. A No. 5 Mayer rod was used for the first coat and then a No'. 8 Mayer rod for the second coat giving a total coating weight in the range of 5 to 7 pounds per 3,000 ft Each coat was dried for 10 to 20 seconds in a forced air oven operating at a temperature of about 250 to 300 F. The minimum heat-seal temperature (MHST) was determined by separately sealing 1-inch wide strips of coated material at varying temperatures using a 10 to 20 PSI heat sealer jaw pressure and 6 to'l second dwell time. The MHST was determined as that temperature required to cause complete fiber tear of the seal as it was pulled apart on a Scott X 5 tensile, tester. i-

The following Table, 111 sets forth theipresence or absence of the sulfonic acid salt and the alkyl phenololefin oxide adduct, as well as the minimum heat-seal temperature (MHST) of each coated sample' TABLE IV What is claimed is:

l. A process for reducing the heat-seal temperature requirements of films and coatings produced from a polymer latex which latex consists essentially of water O O O II II 4 II II I TQQLLMTQLQILAIQT IHQPF fqtlli' which will activate the double bond present in said vinyl group; Q-- is an alkylene and arylene divalent hydrocarbon having from one to about eight carbon atoms and having its valence bonds on different carbon atoms; the symbol M+ represents a cation selected from the group consisting of free acids, alkali metal salts, and ammonium, amine, sulfonium and quaternary ammonium salts, and

3. any remainder being one or more monoethylenically unsaturated comonomers selected from the group consisting of methacrylic acid, methyl methacrylate, hydroxyethylacrylate, hydroxypropylacrylate, hydroxyethylmethacrylate, acrylic acid, acrylonitrile, methacrylonitrile, acrylamide and the lower alkyl and dialkylacrylamides, acrolein, methylvinyl ketone and vinyl acetate, said process comprising: having present in said polymer latex prior to fusion of said latex into a film or coating from about 0.5 to about 5 percent by weight of latex polymer solids of analkyl phenol-olefin oxide adduct having the formula 10 integer from 6 to 40; and where R is hydrogen or methyl. 7 g

2. The process of claim 1 wherein said significantly water-soluble ionic material is sodium sulfoethyl methacrylate..

3. The process of claim 2 wherein said alkyl phenol is selected from the group consisting of ditertiarybutyl phenol, disecondarybutyl phenol and nonyl phenol.

4. The process of claim 3 wherein said olefin oxide is ethylene oxide.

5. The process of claim 3 wherein said olefin oxide is a mixture of ethylene and propylene oxides.

6. The process of claim 4 wherein said polymer latexis prepared from a monomer composition of about 92 parts by weight vinylidene chloride, about S-parts by weight acrylonitrile and about 1.6 parts by weight sodium sulfoethyl methacrylate.

7. The process of claim 4 wherein said polymer latex is prepared from a monomer composition of about 92 parts by weight vinylidene chloride, about 5.5 parts by weight acrylonitrile, about 2.5 parts by weight methyl methacrylate and about 1.4 parts by weight sodium sulfoethyl methacrylate.

8. The process of claim 4 wherein said polymer latex is prepared from a monomer composition of about parts by weight vinylidene chloride, about 15 parts by weight butyl acrylate, about 5 parts by weight acrylonitrile and about 1.6 parts by weight of sodium sulfoethyl methacrylate. 

1. A PROCESS FOR REDUCING THE HEAT-SEAL TEMPERATURE REQUIREMENTS OF FILMS AND COATINGS PRODUCED FROM A POLYMER LATEX WHICH LATEX CONSISTS ESSENTIALLY OF WATER AND A COLLOIDALLY DISPERSED SOLID POLYMER PREPARED BY THE POLYMERIZATION IN AQUEOUS DISPERSION OF
 1. AT LEAST ABOUT 80 PERCENT BY WEIGHT BASED ON THE TOTAL WEIGHT OF MONOMERS USED OF VINYLIDENE CHLORIDE, AND
 2. FROM ABOUT 0.1 TO ABOUT 5 PERCENT BASED ON THE TOTAL WEIGHT OF THE MONOMERS USED OF A SIGNIFICANTLY WATERSOLUBLE IONIC MATERIAL SELECTED FROM THE GROUP OF SULFONIC ACIDS AND THEIR SALTS HAVING THE FORMULA
 2. from about 0.1 to about 5 percent based on the total weight of the monomers used of a significantly water-soluble ionic material selected from the group of sulfonic acids and their salts having the formula R-Z-Q-SO3 -M+ wherein the radical R is selected from the group consisting of vinyl and alpha-substituted vinyl; the symbol Z represents a difunctional linking group of the structure
 2. The process of claim 1 wherein said significantly water-soluble ionic material is sodium sulfoethyl methacrylate.
 3. The process of claim 2 wherein said alkyl phenol is selected from the group consisting of ditertiarybutyl phenol, disecondarybutyl phenol and nonyl phenol.
 3. any remainder being one or more monoethylenically unsaturated comonomers selected from the group consisting of methacrylic acid, methyl methacrylate, hydroxyethylacrylate, hydroxypropylacrylate, hydroxyethylmethacrylate, acrylic acid, acrylonitrile, methacrylonitrile, acrylamide and the lower alkyl and dialkylacrylamides, acrolein, methylvinyl ketone and vinyl acetate, said process comprising: having present in said polymer latex prior to fusion of said latex into a film or coating from about 0.5 to about 5 percent by weight of latex polymer solids of an alkyl phenol-olefin oxide adduct having the formula
 3. ANY REMAINDER BEING ONE OR MORE MONOETHYLENICALLY UNSATURATED COMONOMERS SELECTED FROM THE GROUP CONSISTING OF METHACRYLIC ACID, METHYL METHACRYLATE, HYDROXYETHYLACRYLATE, HYDROXYPROPYLACRYLATE, HYDROXYETHYLMETHACRYLATE, ACRYLIC ACID, ACRYLONITRILE, METHACRYLONITRILE, ACRYLAMIDE AND THE LOWER ALKYL AND DIALKYLACRYLAMIDES, ACROLEIN, MTHYLVINYL KETONE AND VINYL ACETATE, SAID PROCESS COMPRISING: HAVING PRESENT IN SAID POLYMER LATEX PRIOR TO FUSION OF SAID LATEX INTO A FILM OR COATING FROM ABOUT 0.5 TO ABOUT 5 PERCENT BY WEIGHT OF LATEX POLYMER SOLIDS OF AN ALKYL PHENOL-OLEFIN OXIDE ADDUCT HAVING THE FORMULA
 4. The process of claim 3 wherein said olefin oxide is ethylene oxide.
 5. The process of claim 3 wherein said olefin oxide is a mixture of ethylene and propylene oxides.
 6. The process of claim 4 wherein said polymer latex is prepared from a monomer composition of about 92 parts by weight vinylidene chloride, about 8 parts by weight acrylonitrile and about 1.6 parts by weight sodium sulfoethyl methacrylate.
 7. The process of claim 4 wherein said polymer latex is prepared from a monomer composition of about 92 parts by weight vinylidene chloride, about 5.5 parts by weight acrylonitrile, about 2.5 parts by weight methyl methacrylate and about 1.4 parts by weight sodium sulfoethyl methacrylate.
 8. The process of claim 4 wherein said polymer latex is prepared from a monomer composition of about 80 parts by weight vinylidene chloride, about 15 parts by weight butyl acrylate, about 5 parts by weight acrylonitrile and about 1.6 parts by weight of sodium sulfoethyl methacrylate. 